Presently, wireless networks, such as Long Term Evolution (“LTE”) and LTE-Advanced (“LTE-A”) networks, may be heterogeneous networks that include macro cells that provide higher power and wider area coverage and small cells that provide lower power and smaller area coverage than the macro cells. Such wireless networks can also include High-Speed Downlink Packet Access+ (“HSDPA+”) networks, Wideband Code Division Multiple Access (“WCDMA”) networks, CDMA2000 Evolution Voice-Data Optimized (“1xEV-DO”) networks, and other wireless networks.
The small cells can be located within or outside a macro-cell coverage area. The small cells may be provided to offer additional capacity, such as to handle more user equipment, and may be provided to offer additional coverage, such as to fill in coverage holes or gaps in a macro-cell-coverage area. Small cells include micro cells that provide coverage of up to approximately 2 kilometers, such as for large train stations and airports that also may require additional capacity beyond the capacity of a co-located macro cell and for temporary additional network capacity, such as at sporting events and festivals and during emergency situations. Small cells also include pico cells that provide coverage of up to approximately 200 meters, such as for airports, event venues, train stations, stock exchanges, shopping malls, and large office areas. Small cells additionally include femto cells that provide coverage of up to approximately 10 meters, such as for homes and small office areas. Small cells can further include other cells that provide less coverage than a macro cell. A base station, such as an evolved Node B (“eNB”), can be associated with each cell type to provide network access to wireless mobile devices, such as user equipment, passing through the associated cell-coverage area.
The macro cells and the small cells can be multi-state cells in that they can have an active mode and a dormant mode. A neighbor cell is a cell in a power-saving mode and can also be considered an off cell or in a sleep mode. An active cell is a cell in an operational mode and can also be considered an on cell or in an awake mode.
As user equipment travels through small cell-coverage areas, cell handovers may be required. Handover is used to keep user equipment connected to the best base station (“eNodeB”). Handover is usually based on downlink received-signal strength and carrier-to-interference ratio measurements. Processing of the handover measurement is usually done in Layer 1 and Layer 3 (“L3”) by the user equipment, and handover is initiated by the serving eNodeB if certain event criteria are met.
Unfortunately, handovers in the presence of active and dormant cells result in network-system and user-equipment inefficiencies and other problems. These problems include increased detection and reporting of serving-cell channel quality, increased user-equipment power consumption, and excessive handover between cells with an increased risk of radio-link failure. For example, a user equipment cannot engage in efficient radio-link monitoring for a dual-state cell that is in a dormant state.